Filters employing both acidic polymers and physical-adsorption media

ABSTRACT

A filter includes at least two different adsorptive media. First, chemisorptive media, which is porous and includes an acidic functional group, is used to remove molecular bases, including ammonia, organic amines, imides and aminoalcohols, from the atmosphere used in semiconductor fabrication and other processes that require uncontaminated gaseous environments of high quality. Second, physisorptive media is able to adsorb condensable contaminants, particularly those having a boiling point greater than 150 degrees C. The physisorptive media can include untreated, activated carbon.

RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.60/261,928, filed on May 5, 2000, and U.S. Provisional Application No.60/225,248, filed on Aug. 15, 2000. The entire teachings of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In this age of increased air pollution, the removal of chemicals fromthe air we breathe is a concern of everyone. In addition, in thefabrication of electronic materials and of devices such assemiconductors, there is a requirement for uncontaminated air of highquality. To filter contaminants from the air, gas phase filtration iscommonly employed, typically using activated carbon manufactured invarious ways. One approach uses a carbon/adhesive slurry to glue thecarbon to the substrate. The adhesive decreases carbon performance byforming a film on its surface. In another approach, an organic-based webis carbonized by heating, followed by carbon activation. Filtersproduced by such an approach is expensive and has relatively lowadsorption capacity. In yet another approach, a slurry of carbon powdersand fibers is formed into sheets by a process analogous to a wetpapermaking process. This material has a medium-to-high cost, and has anundesirable high pressure drop. Moreover, chemically-impregnated carbonparticles, used for the chemisorption of lower molecular weightmaterials, cannot be efficiently used in conjunction with an aqueousprocess, as the aqueous nature of the process either washes away thechemical used to impregnate the carbon, or reacts undesirably with theimpregnating or active chemical groups thereby rendering it inoperative.In general, however, filter materials that do not incorporatechemically-active groups perform far less effectively for some keylow-molecular-weight components, such as ammonia, in comparison tofilter materials that include chemically-active groups.

SUMMARY OF THE INVENTION

Such filters have been accepted in the industry, and they are presumablyconsidered to perform adequately for their intended purpose. However,they are not without their shortcomings. In particular, none of theseaforementioned prior art approaches fully achieve the desired propertiesthat provide a clean, cost effective, high efficiency, low pressuredrop, adsorptive composite.

The present invention provides a filter which overcomes theseshortcomings. In particular, in one aspect of the invention, afluid-permeable filter includes a conduit through which fluid,particularly gas, can flow. Within the conduit is chemisorptive mediathat includes a copolymer having an acidic functional group forchemically adsorbing a base contaminant in a fluid passing through theconduit. Also within the conduit is physisorptive media for physicallyadsorbing a condensable contaminant from a fluid passing through theconduit. The chemisorptive media and physisorptive media are in separatefilter elements in a preferred embodiment, though the two media typescan alternatively be intermixed to form a single, undivided filter body.

Preferably, the filter is a clean, cost-effective, high-efficiency,low-pressure-drop, gas phase filter comprising a high-surface-area,highly-acidic, chemically-acidic adsorbent in combination withuntreated, or virgin, activated carbon. One embodiment of the inventionemploys a non-woven composite material having acidic functional groupsthat bind to airborne bases. The untreated, activated carbon adsorbsorganic and inorganic condensable contaminants, typically those having aboiling point greater than 150° C. The invention can be used inlithography systems that employ materials that are sensitive toimpurities, such as molecular bases (e.g., ammonia and n-methylpyrrolididnone), and organic and inorganic condensable contaminants(e.g., iodobenzenes and siloxanes), present in the air circulatingthrough semiconductor wafer processing equipment. A large number ofbases including ammonia, NMP, triethylamine pyridine, and others, can bemaintained at concentrations below 2 ppb in a tool cluster filtered withthe present invention. The acidic adsorbent can be formed, for example,by the dry application of an active, acidic adsorbent to a non-wovencarrier material that is then heated and calendered with cover sheets.

The non-woven carrier materials can be polyester non-wovens, and theacidic adsorbent can include sulfonated divinyl benzene styrenecopolymer. One embodiment employs carboxylic functional groups. Theacidic groups have at least 1 milliequivalent/gram of copolymer aciditylevel or higher and preferably at least 4.0 milliequivalents/gram ofcopolymer or higher. The polymers used are porous, and can have a poresize in the range of 50-400 angstroms and a surface area of 20 m²/g orhigher.

The dry processing of a non-woven polyester batting allows for evendistribution of acidic, adsorbent particles throughout the depth of thepolyester batting. This provides an increased bed depth at a very lowpressure drop, which is highly desirable since a twofold increase in beddepth can increase the filter's breakthrough time (time to failure)fourfold when using these thin fabric-based sulfonic beds.

Activated carbon is discussed in greater detail in U.S. Pat. No.5,582,865, titled, “Non-Woven Filter Composite.” The entire contents ofthis patent are incorporated herein by reference. The filter can havetwo (or more) layers, one of activated carbon and one of sulfonateddivinyl benzene styrene copolymer beads. Additionally, two or morematerials can be mixed to provide a composite filter.

Thus, provided herein is a clean, cost-effective, high-efficiency,low-pressure-drop, adsorptive composite filter, and a method for formingsaid composite filter. The composite filter is particularly useful forthe removal of base and organic and inorganic condensable contaminants(typically those with a boiling point greater than 150 degrees C.) in anair stream. Particulates will also be removed if greater than the poresize of the filter. The filter can have a service life of several monthswith a pressure drop to reduce power consumption and minimize impact onthe systems operation. For example, a high-pressure-drop filter canrequire a longer time for a lithography system to equilibrate thetemperature and humidity after filter replacement. In comparison tochemically-treated, activated-carbon filters, the combination filters ofthis invention offer much higher adsorption performance due to thesuperior adsorption properties of untreated, activated carbon overchemically-treated, activated carbon. The use of untreated, activatedcarbon in accordance with methods described herein can provide superiorbreakthrough capacity for organic and inorganic condensable contaminantsbecause the chemical treatment performed on the activated carbon torender it suitable for capturing molecular bases compromises itscapacity for adsorbing organic and inorganic condensable contaminants,typically those with a boiling point greater than 150 degrees C.

In another embodiment, a synthetic carbon material, such as thatdescribed in U.S. Pat. No. 5,834,114, the contents of which areincorporated herein by reference in their entirety, can be coated withthe acidic materials of the present invention to provide a porous acidicfilter element in accordance with the invention. In yet anotherembodiment, the activated nutshell carbon media described in U.S. Pat.No. 6,033,573, the contents of which are incorporated by reference intheir entirety, can be used alone or in combination with any of theother chemisorptive or physisorptive media described herein to removecontaminants from the air flowing through the conduit in the same manneras is taught in this specification.

A detection system and method of use for determining when the filterneeds to be replaced by detecting base contaminants in air is describedin U.S. patent application Ser. No. 09/232,199, entitled, “Detection ofBase Contaminants in Gas Samples,” filed on Jan. 14, 1999, now U.S.Patent No. 6,207,460, with Oleg Kishkovich, et al. as inventors. Also,U.S. patent application Ser. No. 08/795,949, entitled, “Detecting ofBase Contaminants,” filed Feb. 28, 1997, now U.S. Patent No. 6,096,267,with Oleg Kishkovich, et al. as inventors, and U.S. patent applicationSer. No. 08/996,790, entitled, “Protection of Semiconductor Fabricationand Similar Sensitive Processes,” filed Dec. 23, 1997, now U.S. PatentNo. 6,296,806, with Oleg Kishkovich, et al. as inventors, can also beused with the present invention. These patent applications disclose theprotection of a DUV lithography processes using chemically-amplifiedphotoresists that are sensitive to amines in the air. These patentapplications are incorporated in the present application in theirentirety by reference.

One method of fabricating a filter element having a large surface areaand the desired flow characteristics involves the use of a powderedmaterial that is deposited in sequential layers one on top of the other.Following the deposit of each layer of powdered material, a bindermaterial is delivered onto each layer of powdered material using aprinting technique in accordance with a computer model of the threedimensional filter element being formed. Following the sequentialapplication of all of the required powder layers and binder material toform the part in question, the unbound powder is appropriately removed,resulting in the formation of the desired three dimensional filterelement. This technique provides for the fabrication of complex unitaryor composite filter elements having high surface area that are formedwith a very high degree of resolution.

In another apparatus, the physisorptive and chemisorptive filter mediaare positioned in a circulation loop for circulating air through aphotolithography tool. The two media are respectively positioned atdifferent locations such that the physisorptive media will be maintainedat a temperature cooler than that at which the chemisorptive media ismaintained.

The physisorptive media can be positioned upstream from thechemisorptive media (i.e., between the chemisorptive media and an outletof the photolithography tool) and can be positioned proximate to thedownstream side of a cooling coil in the air conditioning unit of thetool. Alternatively, the physisorptive media can be coupled with aseparate cooling element, such as a source of chilled water. In eithercase, the air passing through the physisorptive media can be cooled andthen, after exiting the physisorptive media, reheated to a fixedtemperature and passed through the chemisorptive media beforere-entering the photolithography tool. Temperature sensors can be usedto monitor the temperature of the different media and also providefeedback signals to a controller for closed loop control of the system.The physisorptive filter element can also be contained in a rotatingwheel with separate chambers for active adsorption, regeneration andconditioning. Advantages provided by some of these embodiments includeenhanced removal of lower-molecular-weight condensable contaminants,reduction in the overall footprint of the system, reduction in operatingpressure drop of the filtration component, and significantly increasedtime between change-out or service. Further, lower-molecular-weightorganic contaminants may be removed more effectively with thetemperature-swing beds described herein than is achievable with passiveadsorption beds.

In another aspect of the invention, a filter unit include a multiplicityof filter elements. The filter elements are made of a chemisorptivemedia and a physisorptive media. The filter unit also includes amultiplicity of sampling ports within the filter unit for connecting toa monitor device which monitors the performance of the filter elements.The sampling ports are arranged in a manner with individual samplingports located between adjacent filter elements. There can be samplingport located on an upstream side of the multiplicity of filter elements,and another sampling port located on a downstream side of themultiplicity of filter elements.

In some embodiments, the monitor device is an analytical device, suchas, for example, a gas chromatograph mass selective detector, an ionmobility spectrometer, an acoustic wave detector, an atomic absorptiondetector, an inductance couple plasma detector, or a Fourier transformmethods. Alternatively, the monitor device can be a concentrator whichcollects the sample drawn to the concentrator with a pump, or theconcentrator is coupled to the sample port so that the contaminantsaccumulate in the concentrator by diffusion. Once the sample iscollected in the concentrator, the concentrator is taken to a lab forevaluating the sample. The filter elements can be arranged in a set ofstack which are arranged in a series, and in each stack, the filterelements are arranged in parallel.

In another aspect, a photolithography system includes an air handler formoving air through the system, and delivers unfiltered air to the filterunit, and a photolithography tool which receives filtered air from thefilter unit. A particular advantage of this arrangement is that it isable to detect contaminants before the contaminants reach the lens of aphotolithography tool.

In yet another aspect of the invention, a filter unit includes one ormore filter elements. There can be a sampling port located between twofilter elements. Additionally, or alternatively, there is a samplingport located on one side of a filter element, or there can be a secondsampling port located on an opposite side of the filter element.

Related aspects of the invention include a method for filtering airthrough a filter unit and a method for circulating air through aphotolithography tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 illustrates a filter including a chemisorptive filter element anda physisorptive filter element.

FIG. 2 illustrates a filter, wherein the chemisorptive filter element iscoated on the physisorptive filter element.

FIG. 3 illustrates a filter including an electrostatically-chargednonwoven filter material in addition to the chemisorptive filter elementand physisorptive filter element.

FIG. 4 illustrates a filter of this invention coupled with aphotolithography tool.

FIG. 5 illustrates a filter assembly.

FIG. 6 is a schematic illustration of an apparatus including aphotolithography tool and a circulation loop with physisorptive mediaand chemisorptive media positioned for enhanced contaminant removalefficiency.

FIG. 7 is a schematic illustration of another embodiment of an apparatusincluding a photolithography tool and a circulation loop withphysisorptive media and chemisorptive media positioned for enhancedcontaminant removal efficiency.

FIG. 8 is a perspective view of an acidic, adsorbent filter elementbefore heating and calendaring.

FIG. 9 is a perspective view of the acidic, adsorbent filter elementafter heating and calendaring.

FIG. 10 is a perspective view of the acidic, adsorbent filter elementafter heating and calendaring with a cover sheet.

FIG. 11 is a flow chart illustrating a process for fabricating a filterelement.

FIG. 12 illustrates an example of a three dimensional filter elementfabricated in accordance with the process illustrated in FIG. 11.

FIG. 13 is a perspective view of a filter element in a square orrectangular containment structure showing the creases of the pleatedstructure.

FIG. 14 is a top view of a filter element showing its pleated structure.

FIG. 15 is a top view of a filter element with a highfirst-pass-efficiency multi-pleat pack panel filter in a square orrectangular containment structure.

FIG. 16 is a top view of a filter element in a radially-pleatedcylindrical containment structure.

FIG. 17 is a top view of a filter element in a media-wrapped cylindricalfilter.

FIG. 18 is a perspective view of a process of producing a filterelement.

FIG. 19 is a pleated filter element.

FIG. 20 is a graphical illustration comprising the base removalefficiency of filters previously available and of an acidic, adsorbentfilter element of this invention.

FIG. 21 is a graph illustrating comparative vapor breakthrough rateswith treated and untreated, activated carbon filters.

FIG. 22 is a filter unit in accordance with the invention.

FIG. 23 is a schematic illustration of the filter unit of FIG. 22 as acomponent of a photolithography system.

FIG. 24A is a close-up view of a sampling port of the filter unit ofFIG. 22 connected to an analytical device.

FIG. 24B is a close-up view of a sampling port of the filter unit ofFIG. 22 connected to a concentrator.

FIG. 24C is a close-up view of a passive sampler attached to a samplingport of the filter unit of FIG. 22.

FIG. 25 is a schematic illustration of a sacrificial lens used tomonitor the filters.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows. Afluid-permeable filter includes chemisorptive media and physisorptivemedia. Each of these two types of media can be in separate filterelements. The embodiment illustrated in FIG. 1 includes a chemisorptivefilter element 16 and a physisorptive filter element 32 mounted within aconduit 36. In an alternative embodiment, illustrated in FIG. 2, thechemisorptive filter element 16 can form a layer attached to one or bothsides of the physisorptive filter element 32. Additionally, anelectrostatically-charged nonwoven filter material 34 can cover thechemisorptive and physisorptive filter elements 16, 32, as shown in FIG.3.

The chemisorptive filter element 16 includes porous, chemisorptive mediaformed with a copolymer having an acidic functional group that enablesthe group to react with a reagent. The physisorptive filter element 32includes physisorptive media, such as untreated, activated carbon. Theterm, “untreated,” as used herein, means an activated carbon that hasnot been modified by chemical treatment to perform chemisorption;rather, untreated, active carbon remains as a physical, or nonpolar,adsorbent. The physisorptive media remove organic and inorganiccondensable contaminants, typically those having a boiling point greaterthan 150 degrees C. via physisorption, while the chemisorptive mediaremove base vapors via chemisorption. The term, “physisorption,” refersto a reversible adsorption process in which the adsorbate is held byweak physical forces. In contrast, the term, “chemisorption,” refers toan irreversible chemical reaction process in which chemical bonds areformed between gas or liquid molecules and a solid surface.

As shown in FIG. 4, the filter 40 can be mounted at an inlet of a deepultraviolet photolithography tool 41 (e.g., a stepper or scanner) tofilter air entering the tool 41 and to protect the projection andillumination optics 42 as well as the photoresist on a wafer 44 withinthe chamber 46 of the photolithography tool 41.

The filter can have a variety of constructions. In a first example, abed of polymer pellets and untreated, activated carbon is exposed to theairstream using a traditional media tray and rack system (e.g., a metalenclosure that uses perforated material or screens both to hold in theadsorbent while allowing air to flow through the structure). In a secondexample, the filter is in the form of a honeycomb configuration wherepolymer pellets and untreated, activated carbon are held in apartially-filled or completely-filled honeycomb structure. In a thirdexample, the polymer and untreated, activated carbon form a monolithicporous or honeycomb structure. In a fourth example, a mat of polymerfibers, either woven or nonwoven, incorporate untreated, activatedcarbon and are pleated and arranged into a traditional pleated airfilter. In a fifth example, a bed of activated carbon pellets areexposed to the airstream using a traditional media tray and rack systemwith a layer of nonwoven composite material comprising acidic polymer,comprising a sulfonated copolymer-based composite material attached orincorporated into one side or both sides of the carbon tray. A pleatedarray of filters are illustrated in FIG. 5.

The apparatus illustrated in FIGS. 6 and 7 are designed to removelower-boiling-point contaminants with greater effectiveness and tobetter optimize the separate conditions under which the chemisorptivemedia and physisorptive media operate. By providing better purificationof the airstream entering a photolithography tool, better protection isprovided against photoresist contamination from airborne molecular basesand photo-induced organic contamination of optics surfaces.

In the apparatus of FIG. 6, a circulation loop 102 circulates airthrough the photolithography tool 41. An air conditioning unit 104regulates the temperature and humidity of air entering thephotolithography tool 41 and ensures that the temperature and humidityremain within tightly-prescribed limits. A computer having acomputer-readable medium storing software code for controlling thecooling element (e.g. cooling coils) and heating element can be coupledvia a processor with the air conditioning unit 104 to ensure that thetemperature and humidity are maintained within those limits. Achemisorptive filter element 16 is positioned within the circulationloop to take advantage of the enhanced chemisorption that occurs atwarmer and more humid conditions. Meanwhile, a physisorptive filterelement 32 is positioned to take advantage of the enhanced physisorptionthat takes place under cooler and drier conditions The chemisorptivefilter element 16 is positioned in the circulation loop 102 at aposition downstream from the air conditioning unit 104 and physisorptivefilter element 32. In this embodiment, the chemisorptive filter elementwill therefore be operated at the fixed temperature (e.g., in a range ofabout 21° to about 23° C.) and humidity established for air entering thephotolithography tool 41. Maintaining this fixed temperature in the tool41 is important to minimize temperature-induced lens distortions thatcan lead to aberations.

Air entering the air conditioning unit 104 comprises recirculated airthat has exited the photolithography tool 41 with make-up air (providedto account for inevitable pressure losses) mixed in. In this embodiment,the air can be at about ambient pressure or at a lower pressure. A fan106 is provided in the air conditioning unit 104 to drive the flow ofair through the unit 104 and through the entire circulation loop 102.Cooling coils 108 are positioned downstream from the fan 106 to cool theincoming air. The cooling coils can be cooled by water chilled to about8° C. After being cooled by the cooling coils 108, the air may be at atemperature of about 18° to about 20° C. In the embodiment of FIG. 6,the air then passes through physisorptive filter element 32, which ispositioned next in line. Due to its positioning proximate to anddownstream from the cooling coils 108, the physisorptive filter element32 is operated at a reduced temperature at which adsorption is enhanced.Finally, the air passes through heating element 110, which reheats theair to the desired operating temperature before it is passed throughchemisorptive filter element 16. Accordingly, the cooling coils 108 andheating element 110 of the air conditioning unit 104 are advantageouslyutilized to provide enhanced physisorption and chemisorption in additionto conditioning the temperature and humidity of the air for enhancedoperation of the photolithography tool 41.

In the apparatus of FIG. 7, the physisorptive filter element 32 is inthe form of a rotating wheel about 1 or 2 meters in length and havingthree separate chambers filled with physisorptive filter media. A motor112 is couple with the wheel to rotationally drive it in the directionshown by the arrows (counter-clockwise when viewed from an upstreamposition in the circulation loop 102).

The chamber operating as the active chamber 114 is positioned to receiveair recirculated from the photolithography tool 41 through circulationloop 102. The active chamber 114 will remove contaminants from the airin the circulation loop 102.

The preceding chamber in rotational sequence is operating as theconditioning chamber 116. The conditioning chamber 116 is positioned toreceive chilled water circulated through line 120. The chilled watercools the physisorptive filter media in conditioning chamber 116 so thatthe media will be cooled (providing enhanced adsorptive behavior) beforerotation positions this chamber as the active chamber 114.Alternatively, other cooling elements such as supplemental cooling coilsor a regenerative heat exchanger can be used cool the physisorptivefilter media in the conditioning chamber 116. Other apparatus usingadiabatic cooling of a compressed gas, which is then passed through thebed of physisorptive filter media can also be used.

The remaining chamber, which is operating as the regeneration chamber118, is positioned to receive heat exhaust from the photolithographytool 41. The heat from the heat exhaust will raise the temperature ofthe physisorptive filter media in regeneration chamber 118 and therebycause condensed contaminants to vaporize and release from thephysisorptive filter media rendering the physisorptive filter mediaready for reuse. The released contaminants can then be captured andrecycled. As an alternative to the heat exhaust, other auxilliarysources of heat can be provided to desorb contaminants from the media.

With each one-third rotation, the chamber operating as the activechamber 114 becomes the regeneration chamber 118; the chamber operatingas the regeneration chamber 118 becomes the conditioning chamber 116;and the chamber operating as the conditioning chamber 116 becomes theactive chamber 114. This rotational cycle continues throughout operationof the tool to continually regenerate and cool the physisorptive filtermedia so that “fresh” media will always be available for use. As such,the beds of filter media are operated as “temperature swing adsorptionbeds,” which, in combination with the chemisorptive filter media canmaintain amine levels in the circulated air below 1 part per billion andcan maintain contamination levels of other organics below 1 part perbillion in an apparatus which also maintains temperature (via the airconditioning unit) within +/−17 mK.

This same wheel used as the physisorptive filter element 32 in FIG. 7can likewise be used in the apparatus of FIG. 6. As an alternative tothe rotating wheel embodiment of the physisorptive filter element 32,separate conduits can respectively branch from the circulation loop,heat exhaust, and chilled water conduit into each of the three chambers,and valving at each of the branches can be governed to rotate the flowfrom each conduit through each chamber.

The apparatus of FIGS. 6 and 7 are particularly useful when used tofilter air for a stepper (exposure) tool in a photolithographyapparatus, where the filter elements can remove contaminants that mayform free radicals in the tool, which can then stick to the lens of thetool, thereby fouling its operation. Nevertheless, the apparatus ofFIGS. 6 and 21 can also be used to filter air from a track (whereorganics can change the wettability of a wafer being processed and canthrow off measurements of oxide layer thickness) or to filter airentering other elements in a photolithography apparatus that can beharmed by contaminants. Such uses, which can be combined with the use ofthe apparatus of FIGS. 6 and 7 are further described in U.S. Pat. No.5,833,726, which is hereby incorporated by reference in its entirety.

Referring to FIG. 8, a portion of an acidic, chemisorptive compositefilter element 16 is shown. The chemisorptive composite filter element16 has a cover sheet 66 and a middle layer 62. The cover sheet 66 can bea polyester non-woven fabric having a binder-to-fiber ratio of 55/44 anda thickness of 0.024 inches. The middle layer 62 is an air-laidpolyester non-woven fabric having a thickness of 0.25 inches and abinder to fiber ratio of 35% to 65%. The middle layer 62 is impregnatedwith a porous, acidic, polymer material that binds readily withmolecular bases in air flowing through the filter. Alternatively, thefabrics can be woven.

The structure of FIG. 9 can be used directly in this form as the acidic,adsorbent composite filter element. The acidic, adsorbent composite 16,can employ a second cover sheet 80, provided on the surface of middlelayer 62, opposite to the first cover sheet 66, as shown in FIG. 10. Thecover sheet 66/80 can be a filtering or non-filtering non-wovenpolyester, polyamide or polypropylene material or other similarmaterials. If the cover sheet 66/80 is a filtering material, it servesto provide some filtering of the air entering the composite structurefor removal of particulate materials in the air stream. The cover sheet66/80 can also serve to retain the porous acidic polymer material suchas a sulfonated divinyl benzene styrene copolymer, which can be in beadform, within the middle layer or batting 62. The cover sheets 66/80 canalso be chemically inert materials such as polypropylene or polyester.

The physisorptive filter element 32, shown in FIGS. 1, 6 and 7, caninclude untreated, activated carbon. The carbon is porous (the specificsurface area can be on the order of 1000 m²/g) and can be provided inthe form of fibers. Alternatively, the untreated, activated carbon canbe in the form of particles aggregated in a tray. In another embodiment,the untreated, activated carbon can be formed into a block and heldtogether with a binder material. The untreated, activated carbon can beformed from a variety of sources, including coconut shell, coal, wood,pitch, and other organic sources. Further still, a sulfonated copolymercoating can be attached to the untreated, activated carbon.

Alternatively, high-surface-area filter elements of this invention canbe fabricated using a three-dimensional printing technique as describedin U.S. Pat. Nos. 5,204,055; 5,340,656; and 5,387,380, the entirecontents of these patents being incorporated herein by reference intheir entirety.

Such a method of fabrication of a filter element is illustrated inconnection with FIG. 11. The process 200 includes forming athree-dimensional model 202 of the filter element such that thedimensions are well defined. The first layer of the powder material usedto form the filter is placed 204 by the printer apparatus. A binder isthen delivered 206 onto the powder material resulting in the binding ofselected regions thereof. Steps 204 and 206 are repeated a number oftimes 208 until the high-surface-area filter is formed. Finally, theexcess material is removed 210. An illustrative example of a highsurface area filter made in accordance with this method is shown in theexample 240 of FIG. 12. The binder can be an acid-polymerizable oracid-cross-linkable liquid.

The relative thicknesses of the chemisorptive filter element 16 and thephysisorptive filter element 32 can be engineered so that the usefullife of the two filter elements will be exhausted at approximately thesame time in a given environment. Accordingly, a chemisorptive filterelement formed of sulfonated polymer can be made thinner than aphysisorptive filter element formed of untreated carbon since thephysisorptive properties of the carbon will typically be exhausted morequickly than the chemisorptive properties of the acidic, sulfonatedpolymer.

The two composite filter components 16 and 32, can be contained withinany suitable container(s) or framework(s) for installation in an airflowpath of a filtering apparatus coupled with a photolithography tool, thefilter components 16 and 32 typically being in the form of removable orreplaceable filter elements. For many purposes, it is preferable toincrease the surface area of the filter material exposed to an incidentair flow; and, for this purpose, the composite filter elements can bepleated to provide the increased surface area.

One embodiment is shown in FIG. 13, in which a composite material formsan air filter element 15 or 17. The filter material is pleated into anaccordion-like structure 19, as shown in FIG. 14, contained within asquare or rectangular container 18, having a front 21 and back 23, thatare open to an air stream shown by arrow 22. The pleating 20 issubstantially perpendicular to the air flow. FIG. 9 shows the structurein a front or back view. FIG. 14 shows a cutaway top view of a filterelement.

An alternative embodiment is shown in FIG. 15, wherein a plurality ofpleated composite filter elements 24, are sequentially disposed withincontainer 18, to provide a multi-stage filter through which the air canpass. As in the above embodiment, the pleats 20 of the elements 24 aresubstantially perpendicular to the direction of air flow 22.

A further embodiment is shown in FIG. 16, wherein a composite filterelement is disposed in a cylindrical configuration and retained within acylindrical container 28. The pleats 20 are, as described above,substantially perpendicular to a radially-directed air flow. A furtherembodiment is shown in FIG. 17, wherein the composite structure is woundin a spiral configuration 30 contained within a generally cylindricalcontainer 28.

Acidic, chemisorptive particles can be evenly distributed throughout thenonwoven or fiber matrix or polyester batting. An example of an acidic,chemisorptive particle includes but is not limited to sulfonated divinylbenzene styrene copolymer.

In one embodiment, the ion-exchange, strongly-acidic, preliminarycatalyst has a particle size between 0.3 and 1.2 mm, a porosity ofapproximately 0.30 ml/g, and an average pore diameter of about 250angstroms. The catalyst can have a higher porosity of up to 300 ml/g, orhigher. In addition, the concentration of acid sites in the catalyst canbe approximately 1.8 meq/ml and the surface area of the catalyst can beabout 45 m²/g. Such catalysts are sold under the trade name, AMBERLYST®15DRY or AMBERLYST® 35DRY, by Rohm and Haas. Catalysts with physicalproperties outside the ranges described above can also be used.

Overall, the dry processing of the fiber matrix of the chemisorptivefilter element involves the combination ofsulfonated-divinyl-benzene-styrene copolymers using a dry materialdispensing system, the inherent stratification of the batting's density,and the even distribution of the sulfonated divinyl benzene styrenecopolymer particles as well as stratification of the sulfonated divinylbenzene styrene copolymer particle size. These procedures allow for afabric architecture having an increased bed depth at a very low pressuredrop, which is highly desirable due to the chemisorptive filterelement's high first-pass efficiency coupled with its low operatingcost.

The term, “efficiency,” as employed herein is defined by the formulaX−Y/X wherein X is the upstream concentration of pollutant, and Y is thedownstream concentration of pollutant.

The filter can have a mix of an activated carbon and the preliminarycatalyst material discussed above. This combination has sufficientporosity and strongly acidic groups to provide easy permanent removal ofmedium and strong bases and sufficient retention of weak bases from theairborne base contaminants. The filter can also include a porous polymermaterial.

The filter, as described, is employed in filtering the air inenvironments such as semiconductor fabrication systems where there is arequirement for uncontaminated air of high quality.

Referring to FIG. 18, the middle air-laid polyester non-woven lay 62 iscollated to a cover sheet 66. The acidic, adsorbent particles 60 arepositioned on a fiber matrix 62 from a fluidized bed or other particledistribution system 64. The sulfonated divinyl benzene styrene copolymerparticles 60 are evenly stratified throughout the depth of the batting62. As discussed above, an increased bed depth of adsorbent particlesdistributed throughout the batting is highly desirable as it increasesresidence time, increases exposure of the chemisorptive particlesurfaces, provides a low pressure drop, and substantially increases thelifetime of the filter.

The chemisorptive particles 60 distributed in the matrix 62 are thenheated 74, preferably using two zones 68, 70 of infrared energy atdifferent wavelengths. The batting 62 is heated to an overall averagetemperature of between 250° and 350° F.

The infrared energy causes the chemisorptive particles to adhere to thebatting at points where the particles contact the batting. Thisprocedure avoids the necessity of raising the temperature of the entirebatting to a point at, or near, the melting point of the polyesterbatting, which could cause the batting to melt and collapse therebyencasing the particles and destroying their chemical activity.

The batting 62 is then calendered using a pair of calender rolls 76, 78.The first of these rolls 76 can be temperature controlled, which allowsthe heating and calendering steps to be carried out at a steadytemperature of around 140° F., and prevents overheating and subsequentmelting of cover sheet and prevents over calendering of the fabric. Thesecond roll, roll 78, may be a rubber roll having a durometer thatavoids crushing of the adsorbent particles; roll 78 may also be metal.

Furthermore, when the temperature-controlled roller 76 is used, thepressure at which the batting is about 2000 pounds across the 26-inchdistance. Higher calendering pressures can crush the particlesparticularly when those particles are activated-carbon based, therebyforming dust, which cannot be retained in the composite filter elementand can consequently pass into the gas stream.

In addition, a synthetic non-woven cover sheet 80 that helps to maintainthe sulfonated divinyl benzene styrene copolymer in the batting can becalendered with the batting 62, as discussed above. After the filterelement is formed, gussets or spacers are placed in the filter element.The filter element is sealed into a box.

Optionally, the material may be conducted over an upper roller 84 tofacilitate cooling the material prior to further processing. The methodof manufacture for an activated carbon filter element is described indetail in U.S. Pat. No. 5,582,865, titled, “Non-Woven Filter Composite.”The entire contents of this patent are incorporated herein by reference.

While the above-described method is one method of creating the filter,it is recognized that other techniques can be used. Some of thesetechniques include those developed by Hoechst such as that described inU.S. Pat. No. 5,605,746, the entire contents of which are incorporatedherein by reference or KX Industries' method of media formation. Thecommon feature in all of these methods is the incorporation of achemically-active sorbent into a porous media structure.

In another method, a filter element can be made by premixing thechemisorptive media and the physisorptive media together and thendepositing the mixture onto a web. Or the chemisorptive media and thephysisorptive media can be deposited from a respective dispensing unitin desired proportions onto the web in situ as the web passes beneaththe dispensing units.

A pleated filter structure 220 using the porous acidic polymer of thepresent invention is illustrated in FIG. 19. This is a pleated systemopen on both sides of a rectangular frame 228 with a length 222, width224 and depth such that it can be used as a replacement filter in stackfilter systems. The filter has a removal efficiency of over 99% at 1000ppb challenge concentration.

FIG. 20 graphically illustrates the removal efficiency for threedifferent acidic, chemisorptive filter elements. The graphs representremoval efficiency as a function of time at 20 ppm of NH₃ concentrationupstream from the filter. Filter element size is approximately 12 in.×12in.×6 in. Air flow is approximately 100 cubic feet per minute (cfm).Considering service life data only, it appears that filter element #3performed best. However, if additional data is considered, theconclusion is not so simple. The pressure drop for filter element #1 was0.2″ water column (WC); the pressure drop for filter element #2 was 0.3″WC; and the pressure drop for filter element #3 was 1.0″ WC. Filterelements #1 and #2 are very close to tool manufacturer's specifications,but filter element #3 creates an excessive pressure drop that interfereswith the tool's proper ECU functioning. Excessive pressure drop isundesirable for multiple reasons. For example, it increases fan load andpower consumption, reduces airflow through the tool and positivepressure inside the enclosure. Thus, filter element #1 made inaccordance with the present invention provided a substantial improvementin service life while providing a pressure drop that is compatible withtool operation.

The adsorptive performance of an untreated, activated-carbon filterelement is illustrated in FIG. 21. The graph of FIG. 21 shows theadsorption breakthrough curves for a number of organic compounds on bothtreated and untreated carbons. Comparing the breakthrough curve forethyl acetate (EtAc) for treated 50 and untreated carbon 50′, thecapacity (time to equivalent breakthrough) of untreated carbon is foundto be between 5 and 10 times higher than that of treated carbon. Asshown in the graph, organic vapor capacity for isopropyl alcohol 52 andisobutane 54 in treated carbon is similarly small in comparison tocorresponding measurements of organic vapor capacity for isopropylalcohol 52′ and isobutane 54′ in untreated carbon.

The above-described filter elements have a removal efficiency over 99%for both volatile base compounds and condensable organic contamination.The capacity of these filter elements for both volatile base compoundsand condensable organics has a range between 5 to 60 ppm-days. Theremoval efficiency for non-condensable organic contaminants is greaterthan 90%, and that for element organics is over 99%. Typical elementorganics include Si—R, P—R, B—R, Sn(Bi)₃ and other organo-metallics,where R is an organic group, Si is silicon, P is phosphorous, B isboron, Sn is tin, and Bi is bismuth.

Illustrated in FIG. 22 is an embodiment of the invention as a filterunit 500 including a multiplicity of filter elements 502 having bothchemisorptive and physisorptive media. As can be seen in FIG. 22, thefilter elements 502 are arranged in parallel in a set of stacks 501which are arranged in series within a casing 504 of the filter unit 500.A removable cover panel 505 allows access to the filter elements 502.The filter unit 500 is also provide with a set of casters 507 whichfacilitate easily moving the filter unit 500 to a desired location. Airfiltering systems are described in greater detail in U.S. Pat. No.5,607,647, the entire contents of which are incorporated herein byreference.

In operation, air flows in the direction of arrow A through an intakeport 506, through the filter elements 502, and out of an outlet port508. A set of sampling ports 510-1, 510-2, 510-3, and 510-4(collectively referred to as sampling port 510) provide access toseveral regions of the filter unit 500 to facilitate monitoring thequality of the air as it passes through the filter unit 500. There is asampling port on each side of the individual filter elements 502 so thatthe change in the quality of the air as it goes through the filterelement can be evaluated.

Referring now to FIG. 23, there is shown the filter unit 500 employed inpart of a photolithography process 512. The filter unit 500 is connectedto an air handler unit 514 with a line 516. Another line 518 connectsfilter unit 500 to a tool 520, such as a stepper or track, and a line522 connects the tool 520 to the air handler 514. Thus the air handler514 sends unfiltered air to the filter unit 500 through the line 516.Contaminants in the air are then removed as the air flows through thefilter elements 502 of the filter unit 500. The filtered air issubsequently sent to the tool 520 through the line 518. And after theair passes through the tool 520, it returns via the line 522 back to theair handler 514.

The performance of the filter elements 502 can be monitored by visuallyinspecting the semiconductor wafers. For example, an operator can lookat the wafer to determine if the lithographic process has degraded. Suchdegradation provides an indirect indication to the operator that theperformance of the filters have degraded.

Alternatively, the performance of the filter elements 502 is monitoredby taking samples from the sample ports 510. For example, as illustratedin FIG. 24A, as air flows in the direction of the arrow A through thefilter elements 502, the contaminants in the air in the region betweenthe two filter elements 502 is determined with an analytical device 520which draws samples from the sampling port 510 through a line 522.Typical analytical devices include gas chromatograph mass selective(GCMS), ion mobility spectrometers, surface acoustic wave, atomicabsorption, inductance couple plasma, and Fourier transform (FTIR)methods. Sampling from all the ports 510-1 through 510-4 (FIG. 23),enables determining the amount of contaminants in the air before andafter the air goes through each of the filter elements, therebyproviding a convenient method for monitoring the performance of all thefilter elements 502 of the filter unit 500.

Surface acoustic wave detectors are further described in U.S. Pat. No.5,856,198, which is hereby incorporated by reference in its entirety.Referring to FIG. 25, there is shown an acoustic wave detector 600 usedin combination with a sacrificial lens 602 to detect the presence ofelement organic such as Si—R. The Si—R molecule is volatile; however,upon exposure to UV radiation, Si—R reacts according to the reaction

Si—R→Si—R^(o)+R^(o)

where R^(o) is an organic free radical, and oxygen, O₂, reacts as

O₂→2O^(o)

such that

Si—R^(o)+O^(o)→Si—R—O or R—Si—O

Repeating the above reactions n-times provides

Si—R+O₂→Si—O₂+R+R—O+ . . .

thereby producing Si—O₂, which is a non-volatile inorganic oxide that iscondensable on the sacrificial lens 602. Therefore, by exposing the Si—Rto UV radiation, the acoustic wave detector 600 is able to detect theamount of Si—R in the sampled air.

Rather than connecting the sampling port to an analytical device, thesampling port 510 can be connected to a concentrator 524, as illustratedin FIG. 24B. A pump 526 coupled to the concentrator 524 draws thesamples to the concentrator through a line 528. Alternatively, asillustrated in FIG. 24C, the sample accumulates by diffusion in aconcentrator 530 attached directly to the sampling port 510. In eithercase, the operator takes the concentrator 524 or 530 back to the labwhere the contents of the concentrator is evaluated by any of theanalytical devices described above.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A fluid-permeable filter for a semiconductorprocessing tool comprising: a conduit defining a passage for fluid flowconnected to the processing tool; a first filter element within theconduit, the first filter element having a chemisorptive media includinga porous divinyl benezene styrene copolymer having at least one of asulfonic acid and a carboxylic acid functional group that can chemicallyadsorb a base contaminant in a fluid passing through the conduit; and asecond filter element within the conduit, the second filter elementhaving a physisorptive media able to physically absorb a condensablecontaminant from a fluid passing through the conduit.
 2. The filter ofclaim 1 wherein at least one of the first filter element and the secondfilter element has a honeycomb structure.
 3. The filter of claim 1wherein the acidic group has an acidity level of at least 1milliequivalent/gram of styrene copolymer.
 4. The filter of claim 1wherein the chemisorptive media have a pore size in the range of 50-400angstroms.
 5. The filter of claim 1 wherein at least one of the filterelements is a pleated filter element.
 6. The filter of claim 1 whereinthe media of each filter element have a surface area of 20 m²/g orhigher.
 7. The filter of claim 1 wherein the physisorptive media includeuntreated, activated carbon.
 8. The filter of claim 7 wherein theuntreated, activated carbon fills a tray.
 9. The filter of claim 8wherein the untreated, activated carbon is coconut-shell based.
 10. Thefilter of claim 8 wherein the untreated, activated carbon is coal based.11. The filter of claim 8 wherein the untreated, activated carbon iswood based.
 12. The filter of claim 8 wherein the untreated, activatedcarbon is pitch based.
 13. The filter of claim 8 wherein the untreated,activated carbon is derived from an organic source.
 14. The filter ofclaim 7 wherein the chemisorptive media form a layer attached to theuntreated, activated carbon.
 15. The filter of claim 7 wherein theuntreated, activated carbon is in a block form held together with abinder material.
 16. The filter of claim 1 wherein the chemisorptivemedia and the physisorptive media are in separate filter elements.
 17. Aphotolithography tool comprising: a chamber with optics for directing alight source onto a photoresist-coated substrate; a conduit throughwhich a fluid can be supplied to the chamber; chemisorptive media withinthe conduit, the chemisorptive media including a pourous divinyl benzenestyrene copolymer having at least one of a sulfonic acid and acarboxylic acid functional group that can chemically adsorb a basecontaminant in a fluid passing through the conduit; and physisorptivemedia within the conduit, the physisorptive media being able tophysically adsorb a condensable contaminant from a fluid passing throughthe conduit.
 18. The photolithography tool of claim 17 wherein thephysisorptive media include untreated, activated carbon.
 19. Afluid-permeable filter for a semiconductor processing tool comprising: aconduit defining a passage for fluid flow connected to the processingtool; chemisorptive media within the conduit, the chemisorptive mediaincluding a copolymer having an acidic functional group that canchemically absorb a base contaminant in a fluid passing through theconduit; and physisorptive media within the conduit and intermixed withthe chemisorptive media, the physisorptive media being able tophysically absorb a condensable contaminant from a fluid passing throughthe conduit.
 20. The filter of claim 19 wherein the chemisorptive mediainclude a porous divinyl benzene styrene copolymer having a sulfonicacid group.
 21. The filter of claim 19 wherein the acidic group has anacidity level of at least 1 milliequivalent/gram of styrene copolymer.22. The filter of claim 19 wherein the chemisorptive media have a poresize in the range of 50—400 angstroms.
 23. The filter of claim 19wherein the acidic functional group comprises a carboxylic acid.
 24. Thefilter of claim 19 wherein the chemisorptive media and physisoptivemedia are part of a pleated filter element.
 25. The filter of claim 19wherein the chemisorptive media and physisorptive media each have asurface area of 20 m²/g or higher.
 26. The filter of claim 19 whereinthe physisorptive media include untreated, activated carbon.
 27. Thefilter of claim 26 wherein the untreated, activated carbon fills a tray.28. The filter of claim 27 wherein the untreated, activated carbon iscoconut-shell based.
 29. The filter of claim 27 wherein the untreated,activated carbon is coal based.
 30. The filter of claim 27 wherein theuntreated, activated carbon is wood based.
 31. The filter of claim 27wherein the untreated, activated carbon is pitch based.
 32. The filterof claim 27 wherein the untreated, activated carbon is derived from anorganic source.
 33. The filter of claim 19 wherein the chemisorptivemedia form a layer attached to an untreated, activated carbon.
 34. Thefilter of claim 26 wherein the untreated, activated carbon is in a blockform held togethere with a binder material.
 35. A photolithography toolcomprising: a chamber with optics for directing a light source onto aphotoresist coated substrate; a conduit through which a fluid can besupplied to the chamber; chemisorptive media within the conduit, thechemisorptive media including a copolymer having an acidic functionalgroup that can chemically absorb a base contaminant in a fluid passingthrough the conduit; and physisorptive media within the conduit andintermixed with the chemisorptive media, the physisorptive media beingable to physically absorb a condensable contaminant from a fluid passingthrough the conduit.
 36. The photolithography tool of claim 35 whereinthe chemisorptive media include a porous divinyl benzene styrenecopolymer having a sulfonic acid group.
 37. The photolithography tool ofclaim 35 wherein the physisorptive media include untreated, activatedcarbon.
 38. A fluid-permeable filter for a semiconductor processing toolcomprising: a conduit defining a passage for fluid flow connected to theprocessing tool; a first pleated filter element disposed within theconduit, the first pleated filter element having a chemisorptive mediaincluding a copolymer having an acidic functional group that canchemically absorb a base contaminant in a fluid passing through theconduit; and a second pleated filter element disposed within theconduit, the second pleated filter element having a physisorptive mediaable to physically absorb a condensable contaminant from a fluid passingthrough the conduit.
 39. The filter of claim 38 wherein thechemisorptive media include a porous divinyl benzene styrene copolymerhaving a sulfonic acid group.
 40. The filter of claim 38 wherein theacidic group has an acidity level of at least 1 milliequivalent/gram ofstyrene copolymer.
 41. The filter of claim 38 wherein the chemisorptivemedia have a pore size in the range of 50—400 angstroms.
 42. The filterof claim 38 wherein the acidic functional group comprises a carboxylicacid.
 43. The filter of claim 38 wherein the media of each filterelement have a surface area of 20 m²/g or higher.
 44. The filter ofclaim 38 wherein the physisorptive media include untreated, activatedcarbon.
 45. The filter of claim 44 wherein the untreated, activatedcarbon is coconut-shell based.
 46. The filter of claim 44 wherein theuntreated, activated carbon is coal based.
 47. The filter of claim 44wherein the untreated, activated carbon is wood based.
 48. The filter ofclaim 44 wherein the untreated, activated carbon is pitch based.
 49. Thefilter of claim 44 wherein the untreated, activated carbon is derivedfrom an organic source.
 50. The filter of claim 38 wherein thechemisorptive media form a layer attached to an untreated, activatedcarbon.
 51. The filter of claim 44 wherein the untreated, activatedcarbon is in a block form held together with a binder material.
 52. Thefilter of claim 38 wherein the chemisorptive media and the physisorptivemedia are in separate filter elements.
 53. A photolithography toolcomprising: a chamber with optics for directing a light source onto aphotoresist coated substrate; a conduit through which a fluid can besupplied to the chamber; a first pleated filter element disposed withinthe conduit; the first pleated filter element have a chemisorptive mediaincluding a copolymer having an acidic functional group that canchemically absorb a base contaminant in a fluid passing through theconduit; and a second pleated filter element disposed within theconduit; the second pleated filter element having a physisorptive mediaable to physically absorb a condensable contaminant from a fluid passingthrough the conduit.
 54. The photolithography tool of claim 53 whereinthe chemisorptive media include a porous divinyl benzene styrenecopolymer having a sulfonic acid group.
 55. The photolithography tool ofclaim 53 wherein the physisorptive media include untreated, activatedcarbon.